The purpose of this project is to study cholesterol metabolism in human monocyte-macrophages(MACS). Because MACS are one of the major cell types which accumulate lipid in atherosclerotic lesions, it is of great significance to study lipid metabolism in normal MACS as well as in MACS from patients demonstrating abnormal processing of lipoproteins. MACS accumulated substantial amounts of cholesterol when incubated with nonlipoprotein cholesterol. Interestingly, only a subpopulation of MACS accumulated cholesteryl ester. Cholesteryl ester accumulated in typical lipid droplets but unesterified cholesterol accumulated in a unique cytoplasmic compartment that remains to be identified. Cholesterol-enriched MACS secreted accumulated cholesterol even in the absence of an added cholesterol acceptor by a process that we are now characterizing. We also studied lipid metabolism in MACS from patients with various lipoprotein disorders. ApoE-deficient MACS accumulated nonlipoprotein cholesterol to a much greater extent than normal MACS and showed less efflux than normal MACS, demonstrating that apoE is necessary for normal regulation of MACS cholesterol metabolism. Tangier MACS degrade significantly more HDL in contrast to normal MACS suggesting that these cells could very well be one of the sites where enhanced catabolism of HDL occurs in vivo. Lipoprotein lipase-deficient MACS do not increase their triglyceride content when incubated with VLDL in contrast to normal MACS which do. These studies should provide insight as to how MACS contribute to the metabolism of lipoproteins and cholesterol within human atherosclerotic lesions.